This invention relates to information storage devices, and, more particularly, to the reading of information stored on a magnetic disk.
The modern computer typically has three principal types of components. The processing unit performs computations and manipulations, memory stores instructions and information that is to be processed or has been processed, and input/output devices transmit information into and out of the computer.
There are ordinarily two or three types of memory storage used in the computer. Random access memory is internal to the computer, is usually packaged integrally with the processing unit, and is usually volatile, losing information when power is removed. Information stored in the random access memory is accessible by the processing unit in a very short time. A second type of memory storage is the mass storage device, such as a hard disk, which has a somewhat longer access time but much greater storage capacity. The third type of memory storage is the bulk storage device, typified by tape storage, which has virtually unlimited storage capacity but a much slower access time. Both disk and tape memory are non-volatile, retaining information when power is removed.
The present invention relates to mass storage devices, which can store moderate to large amounts of information with access times typically on the order of milliseconds. In a hard disk storage device, a disk or platter is mounted to rotate in the manner of a conventional phonograph record, typically at a rate of 60 revolutions per second. The parallel faces of the disk are covered with a magnetic storage medium. A read/write head is positioned in close proximity to the surface of the storage medium. A writing device in the head alters the magnetic storage medium to a particular pattern of magnetic states, and a reading device on the same head later reads that same pattern of states to reproduce the information so stored. The information is stored in annular tracks positioned radially outwardly from the center of the disk. The conventional read/write head is movable radially inwardly and outwardly to locate a particular track, and then the information is recorded upon or read from that track. A disk controller operates the disk and read/write functions.
There is a continuing demand for increased memory capacities of the hard disk, increased data readout rates, and decreased access times, as well as for improved reliability. Increased memory capacity is achieved by increasing the diameter of the disk, using both sides of the disk for storage, or stacking several disks together on a common axis in a single unit, and providing read/write heads for each disk that operate in a coordinated fashion. Increased memory capacity can also be achieved by packing more information on each track and more tracks per radial inch. The increased packing demands a greater resolution from the reading head, so that a bit of information can be stored in a smaller area of the disk. This approach, in turn, usually requires that the read sensor in the read/write head be placed closer to the surface of the disk, which serves to decrease the reliability of the disk.
In current disks, the read/write head and the sensors therein are mounted with a separation of less than 1 micrometer from the surface of the rapidly turning disk surface. The close proximity is required because the sensitivity of the memory reading sensor in the head is inadequate to read magnetic fields arising from small areas of the disk surface, when the sensor is placed too far from the disk surface. Disk failures most often occur due to foreign matter such as minute dust particles that lodge between the head and the disk surface and damage the recording medium, or vibrations or bumps that cause the read/write head to impact against the disk surface and damage the medium. With current technology, if the size of the area of each stored bit of information is reduced to increase the packing density of information, the read/write head must be positioned correspondingly closer to the surface of the magnetic storage medium to permit the reading sensor to detect the small magnetic signal emanating from that smaller area, and to distinguish it from the magnetic signal generated by the other nearby stored bits. The closer spacing reduces the disk reliability by increasing the likelihood of contact due to foreign matter or a bump. Thus, the approaches used in the past for achieving improvements cannot be pushed much further due to absolute physical limitations.
Accordingly, a new approach for increasing the memory capacity, reducing the access time, increasing data readout rates, and improving reliability is highly desirable. Such an approach would benefit substantially from maintaining compatibility with existing technology and not requiring a significant change in the computer architecture, but would also be compatible with subsequently developed architectures. The present invention fulfills this need, and further provides related advantages.